1. Field of the Invention
The present invention relates to an image forming apparatus, such as a photocopier, facsimile, printer, plotter, or multifunctional machine having several of such imaging functions, and more particularly, to an electrophotographic image forming apparatus having a transfer unit to transfer an image from a photoconductor or intermediate transfer member to a recording sheet of paper or plastic film, and a fuser unit to fix the transferred image in place on the recording sheet.
2. Discussion of the Background
In electrophotographic image formation, an electrostatic latent image is formed through charging and subsequent optical scanning of a rotating photoreceptive surface such as a drum or belt. Thereafter, a developing device renders the latent image into visible form with toner. The photoconductive surface after development is advanced to a transfer device in which the toner image is transferred to a recording material, such as a paper sheet or plastic film, either directly or via an intermediate transfer member by passing through a transfer nip. Then, the recording sheet is forwarded to a fixing device in which the powder toner image is fused in place, for example, with heat and pressure applied to the recording sheet passing through a fixing nip.
In constructing such an electrophotographic imaging system, proper positioning of the transfer device and the fusing device is fundamental to good imaging and sheet feeding performance of the image forming apparatus. Misalignment of the transfer nip and the fixing nip results in displacement of images produced in the transfer and fixing processes, or curling and wrinkling of recording sheets traveling along the sheet feed path.
Conventional image forming apparatuses are designed with transfer and fuser units individually positioned and supported by a main frame of the apparatus. In order for the two devices to work properly in conjunction with each other, the conventional design requires dimensional control with close tolerances and precise alignment during manufacture, leading to high manufacturing costs and structural complexity. Moreover, even products that meet such high precision requirements can suffer lack of alignment and hence degraded imaging and sheet feeding performance when operated under various different conditions as specified by individual users.